Ultra-light and ultra-accurate portable coordinate measurement machine

ABSTRACT

A portable coordinate measurement machine (CMM) comprises an articulated arm having first and second ends, the articulated arm including a plurality of arm segments and a plurality of rotary joints, the first end configured to connect to a measurement probe and the second end configured to connect to a base. At least one of the rotary joints includes a shaft configured to rotate about an axis of rotation of the at least one of the rotary joints, and a rotary damping mechanism configured to provide controlled damping of rotational movement of the shaft about the axis of rotation.

BACKGROUND

The present disclosure relates generally to a coordinate measuringmachine and more particularly to a high accuracy, ultra-lightweightportable coordinate measuring machine.

Coordinate measurement machines serve to, among other things, measurepoints in a three-dimensional space. Coordinate measuring machines tracethe measuring points in Cartesian coordinate space (x, y, z), forexample. Coordinate measuring machines typically consist of a stand anda tracing system. The stand may serve as a reference point relative towhich the tracing system moves in the space in a measurable manner. Thetracing system for a portable coordinate measuring machine may includean articulated arm attached to the stand at one end and a measurementprobe at the other end.

For the measurement to be useful, it must be accurate. Very highaccuracy, however, is difficult to achieve because of factors such astemperature and load conditions. Particularly in portable coordinatemeasuring machines, warping of the arm caused by thermal changes or bychanges in loads has a negative effect on the measurement's accuracy.Consequently, in terms of their performance, conventional portablecoordinate measuring machines were not nearly as accurate asconventional, non-portable type coordinate measuring machines.

Accuracy Improvements may be available. Conventionally, however, suchimprovements came accompanied by significant increases in mass and/orweight of the coordinate measuring machine. Conventional portablecoordinate measuring machines of improved accuracy were bulky and heavy.These are undesirable characteristics for coordinate measuring machines,particularly portable coordinate measuring machines. Moreover, processesfor constructing and assembling coordinate measuring machines' joints,particularly long joints, with the required precision to obtain accuratemeasurements have not been available.

SUMMARY OF THE INVENTION

The present disclosure provides a portable coordinate measurementmachine (CMM) that is more accurate than prior art coordinate measuringmachines. Remarkably, the CMM disclosed herein is also lighter and lessbulky.

In a first aspect of the invention, the CMM includes rotary joints whoseshaft has no portion with a diameter larger than the inner diameter ofthe joint's bearings and/or whose housing has a bearing engaging portthat has no portion with a diameter narrower than the outer diameter ofthe joint's bearings.

In another aspect of the invention at least one of the rotary jointsincludes a rotary damper operably coupled to the shaft and the housingand configured to provide controlled damping of rotational movement ofthe shaft about the axis of rotation.

In another aspect of the invention rotary damping is built into at leastone of the rotary joints to provide controlled damping of rotationalmovement of the shaft about the axis of rotation.

In another aspect of the invention at least one of the rotary jointsincludes a rotary damping mechanism configured to provide controlleddamping of rotational movement of the shaft about the axis of rotation,and a circuit operably connected to the at least one transducer andconfigured to output a speed and direction signal corresponding to thespeed of the rotational movement of the shaft about the axis of rotationbased on the angle signal and time, the circuit further configured tocompare the speed signal to a predetermined speed threshold to determinewhether the rotational movement occurred at excessive speed resulting inexcessive torque.

In another aspect of the invention at least one of the rotary jointsincludes a rotary damping mechanism configured to provide controlleddamping of rotational movement of the shaft about the axis of rotation,and at least one strain gauge operably coupled to at least one of theshaft and the housing and configured to sense strain on the at least oneof the shaft and the housing due to the rotational movement of the shaftabout the axis of rotation and to output a strain signal that may beused to correct the location of the measurement probe based in part onthe strain signal.

In another aspect of the invention in at least one joint of theplurality of joints a) the shaft that engages the inner diameter of atleast one of the first bearing and the second bearing and b) the port ofthe housing that engages the outer diameter of at least one of the firstbearing and the second bearing are fabricated of steel.

In another aspect of the invention a first joint, from the plurality ofjoints, is attached to a second joint, from the plurality of joints, bya steel structure that is in contact with the inner or outer race of abearing of the first joint or the inner or outer race of a bearing ofthe second joint.

In another aspect of the invention all structural portions of at leastone of the plurality of rotary joints are fabricated of steel.

In another aspect of the invention any structural portions of the CMMincluding the plurality of arm segments and the plurality of rotaryjoints are fabricated of a controlled expansion alloy lighter in weightthan steel and having a thermal expansion coefficient matching that ofsteel or stainless steel in the range of between of 9.9 to 18 μm/m° C.at 25° C.

In another aspect of the invention the measurement probe includes ahandle mechanically but not electrically operably coupled to the firstend, the handle rotatably coupled to the first end to rotate about acentral axis of the measurement probe, the handle including a wirelesstransmitter, and at least one switch button operably connected to thewireless transmitter and configured to, when pressed, cause the wirelesstransmitter to transmit a wireless signal that causes the CMM to take ameasurement.

In another aspect of the invention an electrical circuit includes aserial communication circuit configured without a dedicated capture wireto receive the angle signal and other angle signals from othertransducers in the CMM, the electrical circuit configured to output anagglomeration of the angle signal and the other angle signals to provideinformation corresponding to a position of the measurement proberelative to the base.

In another aspect of the invention the shaft may include a middleportion and first and second end portions fixedly attached to ends ofthe middle portion. The first and second end portions may be concentricto within one tenth of one thousands of an inch (0.0001″). The first endportion engages an inner diameter of the first bearing and the secondend portion engages an inner diameter of the second bearing. The shaftis configured to rotate about an axis of rotation of the first bearingand the second bearing. A first housing end has an inner diameter thatengages an outer diameter of the first bearing and a second housing endhas an inner diameter that engages an outer diameter of the secondbearing. The first and second housing ends may be concentric to withinfive tenth of one thousands of an inch (0.0005″). The first and secondbearings may thus be preloaded to remove play.

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate various example systems, methods,and so on, that illustrate various example embodiments of aspects of theinvention. It will be appreciated that the illustrated elementboundaries (e.g., boxes, groups of boxes, or other shapes) in thefigures represent one example of the boundaries. One of ordinary skillin the art will appreciate that one element may be designed as multipleelements or that multiple elements may be designed as one element. Anelement shown as an internal component of another element may beimplemented as an external component and vice versa. Furthermore,elements may not be drawn to scale.

FIGS. 1A-1C illustrate perspective views of an exemplary coordinatemeasuring machine (CMM). FIG. 1D illustrates a cross-sectional view ofthe exemplary CMM of FIGS. 1A-1C.

FIG. 2 illustrates an exploded view of an exemplary base and swiveljoint of the CMM of FIGS. 1A-1D.

FIGS. 3A and 3B illustrate partial exploded and cross-sectional views,respectively, of an exemplary swivel joint of the CMM of FIGS. 1A-1D.FIGS. 3C and 3D illustrate the process of assembling housing ends to theouter tube of the exemplary swivel joint. FIG. 3E illustrates theprocess of assembling the shaft and bearings to the outer tube of theexemplary swivel joint.

FIG. 4 illustrates an exploded view of an exemplary swivel joint of theCMM of FIGS. 1A-1D.

FIGS. 5A and 5B illustrate exploded and cross-sectional views,respectively, of a hinge joint of the CMM of FIGS. 1A-1D.

FIG. 6A illustrates a cross-sectional view of an exemplary hinge jointof the CMM of FIGS. 1A-1D including a rotary damper.

FIG. 6B illustrates an exploded view of an exemplary instrumented rotarydamper assembly of the CMM of FIGS. 1A-1D.

FIG. 6C illustrates an exploded view of an exemplary non-instrumentedrotary damper assembly of the CMM of FIGS. 1A-1D.

FIG. 7A illustrates a perspective view of an exemplary measurement probeof the CMM of FIGS. 1A-1D.

FIG. 7B illustrates a perspective view of an exemplary alternativemeasurement probe of the CMM of FIGS. 1A-1D.

FIG. 8 illustrates a perspective view of an exemplary on-arm switchassembly of the CMM of FIGS. 1A-1D.

FIG. 9 illustrates a block diagram of exemplary electronics for the CMMof FIGS. 1A-1D.

FIGS. 10A-10E illustrate timing diagrams of exemplary electronics forthe CMM of FIGS. 1A-1D.

FIG. 11A illustrates an exemplary orbit plot showing rotation of a shaftfor a conventional long arm joint. FIG. 11B illustrates an exemplaryorbit plot showing rotation of a shaft for a long arm joint of the CMMof the present disclosure.

DETAILED DESCRIPTION

FIGS. 1A-1C illustrate perspective views of an exemplary coordinatemeasuring machine (CMM) 1. FIG. 1D illustrates a cross-sectional view ofthe exemplary CMM 1. CMM 1 includes an articulated arm 2, a base 4, anda measurement probe 6. The articulated arm 2 is attached at one end tothe base 4 and at the other end to the measurement probe 6. The base 4may include, for example, a magnetic holder 5 to attach the arm 2 to,for example, a working surface. Articulated arm 2 includes two armsegments 8, 9 and a number of rotary joints 12, 14, 16, 18, 20, 22, 24.The CMM 1 may also include an on-arm switch assembly 10.

The overall length of articulated arm 2 and/or the arm segments 8, 9 mayvary depending on its intended application. In one embodiment, thearticulated arm may have an overall length of about 48 inches. This armdimension provides a portable CMM which is well suited for measurementsnow accomplished using typical hand tools such as micrometers, heightgages, calipers and the like. Articulated arm 2 could have smaller orlarger dimensions.

The rotary joints generally include two types of joints, swivel joints12, 16, 20, 24 and hinge joints 14, 18, 22. The swivel joints 12, 16,20, 24 are positioned generally axially or longitudinally along the arm2. The hinge joints 14, 18, 22 are positioned generally at 90° to theswivel joints or 90° to the longitudinal axis of the arm 2. The swiveland hinge joints are generally paired up as shown in FIGS. 1A-1 D butthe joints may be arranged in other configurations. Because of themultiple rotary joints, the arm 2 is manually-positionable meaning thata user is free to manually move the probe 6 to virtually any positionwithin a radius anchored at the base 4 of the CMM 1. Each of thesejoints are generally shown in FIGS. 2-6A.

In general, the magnetic holder 5 of the base 4 attaches the CMM 1 to aworking surface, the base 4 includes the swivel joint 12, which attachesto the hinge joint 14, which attaches to the swivel joint 16, whichattaches to the hinge joint 18, which attaches to the swivel joint 20,which attaches to the hinge joint 22, which attaches to the swivel joint24, which attaches to the measurement probe 6.

FIG. 2 illustrates an exploded view of exemplary base 4 and swivel joint12. FIG. 2 also illustrates the base enclosure 4 a, which has mountedthereon a battery receptacle 26. The CMM 1 is portable and, therefore,may be operated on battery power from a battery (not shown) installed tothe CMM 1 via the receptacle 26. The CMM 1 may also include a power jack25 to which a power adapter may be connected to power the CMM 1.

The swivel joint 12 may include housing 28, shaft 30, bearings 32, 34,encoder printed circuit board (PCB) 36, encoder disk 38, and slip ring40. The swivel joint 12 may also include dust covers 42 a-c and varioushardware such as the threaded studs 44 a-c and screws 47 a-c. Swiveljoints in general are discussed in detail below in reference to swiveljoint 16.

FIG. 3A illustrates partial exploded views of exemplary swivel joint 16while FIG. 3B illustrates partial cross-sectional views of swivel joint16. Each of the figures illustrates only the ends of the swivel joint16; the middle portion of the swivel joint not illustrated correspondsto the arm segment 8. The swivel joint 16 will be used here to describeswivel joints 12, 16, 20, 24 in general even though the swivel jointsmay not be identical. The swivel joints 16 and 20 are very similar.Swivel joint 24 is also similar to swivel joints 16 and 20 except that,as described below, swivel joint 24 has a shorter shaft. At least someof the components of swivel joint 16 are substantially similar tocomponents discussed in detail above in reference to swivel joint 12 andthus these similar components are identified in FIGS. 3A and 3B with thesame reference designators as in FIG. 2.

The swivel joint 16 may include housings 48, 49, shaft portions 50 a, 50b, and 50 c, bearings 32, 34, encoder PCB 36, encoder disk 38, and slipring 40. The bearings 32, 34 are preferably steel or stainless steelball bearings. The shaft portions 50 a and 50 c may be operably attachedto the ends of the shaft portion 50 b to form a shaft assembly 50 asdescribed in detail below. The shaft portion 50 b, being relatively longmay be fabricated of rigid yet relatively lighter material such as, forexample, carbon fiber, aluminum, etc. as well as from steel. The shaftportions 50 a and 50 c, however, may be fabricated of steel to match thematerial from which the bearings 32, 34 are fabricated. Similar to therelatively long shaft portion 50 b, the tube 60 within which the shaftportion 50 b resides may be fabricated of the same rigid yet relativelylight material as shaft portion 50 b as well as from steel. The swiveljoint 16 may also include covers 62 a-b and various hardware such as thesnap rings 64 a-c.

At one end of the swivel joint 16, the housing 48 has a surface 48 athat operably attaches to one end of the tube 60 of the correspondingarm segment (arm segment 8 in the case of swivel joint 16). The housing48 also has a shaft connecting portion 48 c that operably connects theswivel joint 16 to the previous hinge joint (see FIGS. 1A-1D). In thecase of swivel joint 16, the shaft connecting portion 48 c connects theswivel joint 16 to the shaft of the hinge joint 14. At the other end ofthe swivel joint 16, the housing 49 has a surface 49 a that operablyattaches to a second end of the tube 60 of the corresponding arm segment(arm segment 8 in the case of swivel joint 16). The housing 49 also hasa port 49 b within which an end of the shaft assembly resides,particularly shaft portion 50 a. Assembly of the tube 60 to the housingends 48 and 49 is described in more detail below.

As may be best seen in FIG. 3B, at one end of the swivel joint 16, theinner diameter 65 of the port 48 b of the housing 48 engages (e.g.,fixedly attaches to) the outer diameter or outer race of the bearing 32.The port 48 b of the housing 48 may, for example, be glued to the outerdiameter or outer race of the bearing 32. The shaft portion 50 c, forits part, has an outer diameter 67 that engages (e.g., is fixedlyattached to) the inner diameter or inner race of the bearing 32. Theshaft portion 50 c may, for example, be glued to the inner diameter orinner race of the bearing 32. At the other end of the swivel joint 16,the inner diameter 69 of the port 49 b of the housing 49 engages (e.g.,fixedly attaches to) the outer diameter or outer race of the bearing 34.The port 49 b of the housing 49 may, for example, be glued to the outerdiameter or outer race of the bearing 34. The shaft portion 50 a, forits part, has an outer diameter 71 that engages (e.g., is fixedlyattached to) the inner diameter or inner race of the bearing 34. Theshaft portion 50 a may, for example, be glued to the inner diameter orinner race of the bearing 34. The shaft assembly 50, therefore, rotatesabout the axis of rotation a of the bearings 32 and 34 and the housings48 and 49.

The PCB 36 of the swivel joint 16 has installed thereon at least onetransducer configured to output an angle signal corresponding to anangle of rotation of the shaft assembly 50 relative to the housing 48,49 about the axis of rotation a. Each transducer comprises an opticalencoder that has two primary components, a read head 68 and the encoderdisk 38. In one embodiment, two read heads 68 are positioned on PCB 36.In the illustrated embodiment, the encoder disk 38 is operably attachedto an end of the shaft assembly 50 (e.g., using a suitable adhesive)spaced from and in alignment with read heads 68 on PCB 36, which isoperably attached to the housing 48 (e.g., using a suitable adhesive).The locations of disk 38 and read heads 68 may be reversed whereby disk38 may be operably attached to housing 48 and read heads 68 rotate withshaft assembly 50 so as to be rotatable with respect to each other whilemaintaining optical communication. Encoders are commercially availablefrom, for example, Celera Motion under trade names such as MicroEencoders. Each PCB 36 may additionally include a processor for receivingand processing angle signals received from the read heads 68, and atransceiver and connector 93 for connecting the PCB 36 to thecommunication bus of the CMM 1 and/or other wiring as will be discussedhereinafter. Each of the PCB 36 may also include a temperature sensorconnected to the processor to provide for thermal compensation due toroom temperature variation.

The cover 62 b operably attaches to the housing 48 to cover and seal thePCB 36 and encoder disk 38 from dust contamination. The cover 62 aoperably attaches over the cover 62 b and portions of the housing 48 andtube 60 for cosmetic appearance. The cover 62 b has the opening 63 fromwhich the shaft connection portion 48 c of the housing 48 protrudes tooperably connect the swivel joint 16 to the hinge joint 14.

Swivel joint 16 (as well as other joints in CMM 1) may have unlimitedrotation, meaning that it may rotate 360° about its axis of rotation a.Thus, slip ring 40 is used and provides unlimitedly rotatable electricalconnections to swivel joint 16. Shafts used herein in swivel joints suchas the shaft 30 of base swivel joint 12 and the shaft assembly 50 ofswivel joint 16 may be hollow (i.e., have an axial opening 51). Shaftsused herein in hinge joints such as the shaft 80 of hinge joint 18described below may also be hollow and may also include an aperture 81(see FIG. 5B). Back to FIGS. 3A and 3B, as illustrated, the housingcover 62 a has the opening 63, the cover 62 b has the opening 61, andthe housing 48 has the opening 48 d which aligns with the aperture 81 ofthe shaft 80 of the hinge joint 18. Thus, communication bus wiring mayenter the swivel joint 16 from the aperture 81 of hinge joint 14,through the opening 48 d, through the opening 63, the opening 61 andconnect to PCB 36, which connects to the slip ring 40. From the slipring 40, wiring may travel through the axial opening 51 of the shaft 50to the next hinge joint. Such wiring is shown diagrammatically below.

Conventionally a shaft used in a joint for a coordinate measuringmachine had one or more shoulders or flanges extending radiallyoutwardly from the axis of the joint beyond the surface of the shaftthat engages the inner diameter or inner race of the bearing. Theseshoulders or flanges were deemed necessary to retain the shaft axiallyin place in relation to the rest of the joint particularly the joint'sbearings. Similarly, conventionally a housing used in a joint for acoordinate measuring machine had one or more shoulders or flangesextending radially inwardly towards the axis of the joint beyond thesurface of the housing that engages the outer diameter or outer race ofthe bearing. These shoulders or flanges were deemed necessary to retainthe housing axially in place in relation to the rest of the jointparticularly the joint's bearings. See, for example, FIGS. 10, 12, 14,and 16 of U.S. Pat. No. 8,607,467 (which is hereby incorporated byreference in its entirety) in which both shafts and housings haveshoulders or flanges to retain the shafts and housings axially in placein relation to the bearings.

These conventional shafts and housings were manufactured by machining inorder to produce the shoulders or flanges. But even the most advancedmachining processes were limited in the precision they could impart tosuch machined shafts and housings. These parts were, therefore,significantly limited by the precision of the machining process. Thiswas a problem since, as discussed in the Background section of thepresent application, accuracy is important for coordinated measuringmachines.

As best seen in FIG. 3B, the shaft portions 50 a and 50 c have noportion whose diameter is larger than the inner diameter or inner raceof the bearings 32, 34. No portion of the shaft portion 50 a has alarger diameter than the outer diameter 71, which engages the innerdiameter or inner race of the bearings 34. No portion of the shaftportion 50 c has a larger diameter than the outer diameter 67, whichengages the inner diameter or inner race of the bearings 32. Similarly,the port 48 b, which engages the outer diameter or outer race of thebearing 32, has no portion whose diameter is smaller or narrower thanthe outer diameter of the bearing 32. The port 49 b, which engages theouter diameter or outer race of the bearing 34, has no portion whosediameter is smaller or narrower than the outer diameter of the bearing34. Therefore, it may be said that the shaft assembly 50 and housings 48and 49 are shoulderless as that term is defined herein. The shaftportions 50 a and 50 c have no portion extending radially outwardly fromthe axis a of the joint 16 beyond the surfaces 67, 71 that engage theinner diameters or inner races of the bearings 32, 34. Similarly, thehousings 48, 49 have no portion extending radially inwardly towards theaxis a of the joint 16 beyond the surfaces 65, 69 of the housings 48,49, respectively, that engage the outer diameters or outer races of thebearing 32, 34.

Instead of shoulders or flanges, the shaft portions 50 a and 50 c mayhave grooves 72, 73 machined or otherwise formed thereon. The snap rings64 b-c may engage the grooves 72, 73 to retain the shaft assembly 50axially in place in relation to the rest of joint 16 and the bearings32, 34. Similarly, the housing 49 may have a groove 74 machined orotherwise formed thereon. The snap ring 64 a may engage the groove 74 toretain the housing 49 axially in place in relation to the rest of joint16 and the bearings 32, 34. In one embodiment, instead of or in additionto the combination of the grooves 72, 73 and the snap rings 64 b-c toretain the shaft 50 axially in place in relation to the rest of joint 16and the bearings 32, 34, the shaft 50 may be fixedly attached to theinner diameters or inner races of the bearings 32, 34 by use of anadhesive. Similarly, in one embodiment, instead of or in addition to thecombination of the groove 74 and the snap ring 64 a to retain thehousing 49 axially in place in relation to the rest of joint 16 and thebearings 32, 34, the surface 71 of the housing 49 may be fixedlyattached to the outer diameter or outer race of the bearing 34 by use ofan adhesive.

Shoulderless shafts and housings such as those illustrated in FIGS. 3Aand 3B may be manufactured by grinding and honing processes that may bean order of magnitude more precise than machining process used tomanufacture the shouldered or flanged shafts and housings of the priorart. The shoulderless shafts and housings disclosed herein may thus besignificantly more precisely built resulting in significant improvementsin the precision of measurements that may be achieved at the joint 16and similar joints of the CMM 1. In part because of the shoulderlessshafts and housings disclosed herein, the CMM 1 achieves significantlybetter accuracy than prior art portable coordinate measurement machines.

The swivel joint 16 of arm segment 8 is a relatively long joint ascompared to, for example, joint 14 as may be appreciated from FIGS.1A-1D and 3A. The bearings 32 and 34 are located far apart. The shaft 50has three parts, the middle portion 50 b having end portions 50 a and 50c attached to the ends of the middle portion 50 b far apart from eachother. The outer tube 60 is long with housing ends 48 and 49 spaced farapart from each other. Such relatively long joints, and particularlylong joints with multi-portioned shafts, have conventionally not beenable to be constructed such that joint rotation remains precise,particularly when compared to shorter, single-portion shaft, joints.

FIG. 11A illustrates an orbit plot showing typical behavior of rotationof a conventional long arm's shaft measured as prescribed by Orton (P.A. Orton et al, Automatic Self-Calibration of an Incremental MotionEncoder, IEEE Instrument and Measurement Technology Conference,Budapest, Hungary, May 21-23, 2001, at 1614) incorporated here byreference in its entirety. The technique measures, not only angularposition of the shaft, but also horizontal and vertical motion of theshaft. See also U.S. Pat. No. 5,596,189 issued on Jan. 21, 1997incorporated here by reference in its entirety. Notice on the orbit plotof FIG. 11A that horizontal and vertical displacement of theconventional shaft during rotation is about 20 microns from center.Moreover, notice that the horizontal and vertical displacement ofconventional shafts during rotation is non-circular and inconsistentfrom one rotation to the next, varying as much as approximately 5microns. In actuality, horizontal and vertical displacement ofconventional shafts (and particularly long, multi-portion shafts) duringrotation is typically even larger than 20 microns from center,non-circular, and varies from rotation to rotation even more than 5microns. This shaft displacement from center negatively affects accuracyof measurements taken by conventional coordinate measuring machines. Atleast part of the problem causing such undesirable displacement fromcenter is that, up to this point, there has not been a process forconstructing and assembling long, multi-portion shaft, joints with therequired precision.

FIGS. 3C and 3D illustrate an exemplary process for assembling the outertube 60 of the exemplary swivel joint 16 to the housing ends 48 and 49.As shown in FIG. 3C, a fixturing tube FT may be used to promoteprecision in assembling the outer tube 60 to the housing ends 48 and 49.The fixturing tube FT may, for example, be precisely grinded to nearperfect dimensions so that it is cylindrical to within one tenths ofthousands of an inch (0.0001″). Its outer diameter is concentric towithin one tenths of thousands of an inch (0.0001″). The housing ends 48and 49 may be glued to respective ends of the tube 60 and the fixturingtube FT may be used to precisely fix the housing ends 48 and 49 in placerelative to each other while the glue cures. As seen in FIG. 3D (ahalfway cross-sectional view), the housing ends 48 and 49 may be fixedto the tube 60 with the fixturing tube FT inside the assembly. The innerwalls 65 and 69 of the housing ends 48 and 49 may be made to fit tightly(very tightly, almost interference) against the walls FTa and FTb of thevery precise fixturing tube FT. Once the glue has cured, the fixturingtube FT may be removed from the assembly. The fixturing tube FT may beoiled to aid in its removal. Using this process, the housing ends 48 and49 may be made to be concentric (i.e., their inner diameters share thesame axis a) to within five tenths of thousands of an inch (0.0005″).Other methods that may be used to achieve similar results may includeinternal grinding of the housing ends 48 and 49 once affixed to theassembly including the tube 60.

FIG. 3E illustrates an exemplary process for assembling the shaftassembly 50 and the bearings 32 and 34 to the assembly including theouter tube 60 and the housing ends 48 and 49.

First, as described above, the shaft ends 50 a and 50 c may be attachedto the shaft portion 50 b to form the shaft assembly 50. To promoteprecision, the shaft ends 50 a and 50 c may be first machined oversizedby a few thousands of an inch. That is, the shaft ends 50 a and 50 c maybe first made to be wider (larger outer diameter) than their finaldesired diameter. The shaft ends 50 a and 50 c may then be glued to thetwo ends of the long shaft portion 50 b using, for example, v-blocks ona granite table. Next the shaft assembly 50 may be grinded at the twoends 50 a and 50 c so that the two ends are concentric (i.e., theirouter diameters share the same axis a) to within one tenth of thousandsof an inch (0.0001″).

The inner snap rings 64 b and 64 c may be installed to shaft assembly 50at grooves 72 and 73, respectively. The inner races or inner diameters32 a and 34 a of the bearings 32 and 34 may be press fitted to the shaftassembly 50 until they are against snap rings 64 b and 64 c and glued tothe shaft assembly 50. Outer snap ring 64 a may be installed to the endhousing 49 at the groove 74. The assembly including the shaft assembly50 and the bearings 32 and 34 may be inserted into the assemblyincluding the tube 60 and the end housings 48 and 49. Glue may be usedto adhere the outer races 32 b and 34 b of the bearings 32 and 34 to theinner diameters 65 and 69 of the end housings 48 and 49. Then a preload(e.g., 5 or 10 lb weight) may be applied to the outer race 32 b ofbearing 32 to remove play between the inner and outer races of thebearings 32 and 34. In FIG. 3E, the preload PREL is applied to the outerrace 32 b of bearing 32 using the preload application tools PLT1 andPLT2, which ensure that the preload is applied only to the outer race 32b and not the inner race 32 a. The preload PREL is applied to the outerrace 32 b until the glue has cured and then removed. Application of thepreload PREL results in removing play from the bearing assembly.

Conventional processes for constructing and assembling long (andparticularly multi-portion shaft) joints did not allow for the precisionnecessary to effectively preload the bearings to remove play, whichcaused excessive horizontal and vertical displacement of theconventional shaft during rotation. Attempts to preload such impreciseconventional long joints to remove play would result in either excessivedeformation of the bearings, jamming, grinding, excessive wear, etc.(i.e., the joints would not be usable or perform unsatisfactorily) orinsufficient preloading resulting in excessive shaft displacement fromcenter during rotation.

FIG. 11B illustrates an orbit plot showing typical behavior of rotationof a long arm 8 including the multi-portion shaft joint 16 as measuredas prescribed by Orton. Notice that, on the orbit plot of FIG. 11B,horizontal and vertical displacement of the shaft 50 during rotation hasbeen significantly reduced to within 1.5 microns from center. Moreover,notice that the horizontal and vertical displacement of the shaft 50during rotation is remarkably circular and consistent from one rotationto the next. This is a significant improvement from the measureddisplacement exemplarily shown on FIG. 11A for the conventional longjoint. This significant improvement in displacement from centerdrastically improves accuracy of measurements taken by the CMM 1 whencompared to conventional coordinate measuring machines. The processdescribed above for constructing and assembling the long joint 16including the multi-portion shaft 50 provides the required precision toachieve such significant improvements.

FIG. 4 illustrates an exploded view of an exemplary swivel joint 24.Swivel joint 24 is similar to swivel joints 16 and 20 described aboveexcept that swivel joint 24 has a shorter shaft 50 whose lengthcorresponds to the distance between swivel joint 24 and probe 6 beingshorter than the distance between, for example, swivel joint 16 andhinge joint 18. Thus, the probe 6 rotates about the axis a of the swiveljoint 24 and the swivel joint 24 detects the angle of rotation of theprobe 6, which is attached to the end of the swivel joint 16. See FIGS.1A-1D.

FIG. 5A illustrates an exploded view of exemplary hinge joint 18 whileFIG. 5B illustrates a cross-sectional view of hinge joint 18. The hingejoint 18 will be used here to describe hinge joints 14, 18, 22 ingeneral even though the hinge joints may not be identical. At least someof the components of hinge joint 18 are substantially similar tocomponents discussed in detail above in reference to swivel joints 12and 16 and thus these similar components are identified in FIGS. 5A and5B with the same reference designators as in the previous figures.

The hinge joint 18 may include housing 78, shaft 80, bearings 32, 34,encoder PCB 36, and encoder disk 38. The housing 78 has an opening 78 bto which the shaft of the previous swivel joint (shaft 50 of swiveljoint 16 in the case of hinge joint 18) connects. The hinge joint 18 mayalso include covers 82 a-c and various hardware such as the snap rings64 a-c and cap 66.

As may be best seen in FIG. 5B, the housing 78 has ports 87 that engage(e.g., fixedly attach to) the outer diameters or outer races of thebearings 32, 34. The ports 87 of the housing 78 may, for example, beglued to the outer diameter or outer race of the bearings 32 and 34. Inthe embodiment of FIGS. 5A and 5B the housing 78 has two ports 87. Theshaft 80, for its part, has an outer diameter 85 that engages (e.g., isfixedly attached to) the inner diameter or inner race of the bearings32, 34. The shaft 80 may, for example, be glued to the inner diameter orinner race of the bearings 32, 34. The shaft 80, therefore, rotatesabout the axis of rotation b of the bearings 32 34 and the housing 78 ofthe hinge joint 18.

Similar to the swivel joints discussed above, the PCB 36 of the hingejoint 18 has installed thereon at least one transducer configured tooutput an angle signal corresponding to an angle of rotation of theshaft 80 relative to the housing 78 about the axis of rotation b. Eachtransducer comprises an optical encoder that has two primary components,a read head 68 and the encoder disk 38. In the illustrated embodiment,two read heads 68 are positioned on PCB 36. In the illustratedembodiment, the encoder disk 38 is operably attached to an end of theshaft 80 (e.g., using a suitable adhesive) spaced from and in alignmentwith read heads 68 on PCB 36, which is operably attached to the housing78 (e.g., using a suitable adhesive). The locations of disk 38 and readheads 68 may be reversed whereby disk 38 may be operably attached tohousing 78 and read heads 68 rotate with shaft 80 so as to be rotatablewith respect to each other while maintaining optical communication.

The cover 82 b operably attaches to the housing 78 to cover and seal thePCB 36 and encoder disk 38 from dust. The covers 82 a and 82 c operablyattach to each other at one end of the shaft 80 and the cap 66 caps tothe opposite end of the shaft 80 to protect the bearings.

Communications bus wiring may enter the hinge joint 18 from the axialopening 51 of the shaft 50 of the previous swivel joint through theopenings 78 b, 78 c of the housing 78. The wiring may then connect tothe PCB 36 and depart the hinge joint 18 through the axial opening 80 aand the aperture 81 of shaft 80. Such wiring is shown diagrammaticallybelow.

As discussed above, conventionally a shaft used in a joint for acoordinate measuring machine had one or more shoulders or flangesextending radially outwardly from the axis of the joint beyond thesurface of the shaft that engages the inner diameter or inner race ofthe bearing. These shoulders or flanges were deemed necessary to retainthe shaft axially in place in relation to the rest of the jointparticularly the joint's bearings. Similarly, conventionally a housingused in a joint for a coordinate measuring machine had one or moreshoulders or flanges extending radially inwardly towards the axis of thejoint beyond the surface of the housing that engages the outer diameteror outer race of the bearing. These shoulders or flanges were deemednecessary to retain the housing axially in place in relation to the restof the joint particularly the joint's bearings. See, for example, FIGS.10, 12, 14, and 16 of U.S. Pat. No. 8,607,467 in which both shafts andhousings have shoulders or flanges to retain the shafts and housingsaxially in place in relation to bearings.

These conventional shafts and housings were manufactured by machining inorder to produce the shoulders or flanges. But even the most advancedmachining processes were limited in the precision they could impart tosuch machined shafts and housings. These parts were limited by theprecision of the machining process and, as discussed in the Backgroundsection of the present application, accuracy is important for CMM.

As best seen in FIG. 5B, the shaft 80 has no portion whose diameter islarger than the inner diameter or inner race of the bearings 32, 34. Noportion of the shaft 80 has a larger diameter that the outer diameter85, which engages the inner diameters or inner races of the bearings 32,34. Similarly, the ports 87, which engage the outer diameters or outerraces of the bearings 32, 34, have no portion whose diameter is smalleror narrower than the outer diameter of the bearing 32 or the outerdiameter of the bearing 34. Therefore, it may be said that the shaft 80and housing 78 are shoulderless as defined herein i.e., 1) the shaft 50has no portion extending radially outwardly from the axis b of the joint18 beyond the surface 85 of the shaft 80 that engages the innerdiameters or inner races of the bearing 32, 34, and 2) the housing 78has no portion extending radially inwardly towards the axis b of thejoint 18 beyond the surface 87 of the housing 78 that engages the outerdiameters or outer races of the bearing 32, 34.

Instead of shoulders or flanges, the shaft 80 may have grooves 72machined or otherwise formed thereon. The snap rings 64 b-c may engagethe grooves 72 to retain the shaft 80 axially in place in relation tothe rest of joint 18 and the bearings 32, 34. Similarly, the housing 78may have a groove 74 machined or otherwise formed thereon. The snap ring64 a may engage the groove 74 to retain the housing 78 axially in placein relation to the rest of joint 18 and the bearings 32, 34. In oneembodiment, instead of or in addition to the combination of the grooves72 and the snap rings 64 b-c to retain the shaft 80 axially in place inrelation to the rest of joint 18 and the bearings 32, 34, the shaft 80may be fixedly attached to the inner diameters or inner races of thebearings 32, 34 by use of an adhesive. Similarly, in one embodiment,instead of or in addition to the combination of the groove 74 and thesnap ring 64 a to retain the housing 78 axially in place in relation tothe rest of joint 18 and the bearings 32, 34, the ports 87 of thehousing 78 may be fixedly attached to the outer diameters or outer racesof the bearings 32, 34 by use of an adhesive.

Shoulderless shafts and housings such as those illustrated in FIGS. 5Aand 5B may be manufactured by grinding and honing processes that may bean order of magnitude more precise than machining process used tomanufacture the shouldered or flanged shafts and housings of the priorart. The shoulderless shafts and housings disclosed herein may thus besignificantly more precisely built resulting in significant improvementsin the precision of measurements that may be achieved at the joint 18and similar joints of the CMM 1. In part because of the shoulderlessshafts and housings disclosed herein, the CMM 1 achieves significantlybetter accuracy than prior art portable coordinate measurement machines.

Joints for prior art coordinate measurement machines were manufacturedmostly of aluminum or other lightweight materials. See, for example,U.S. Pat. No. 8,607,467 which discloses a coordinate measurement machinein which joints are constructed of cast or machined aluminum components,lightweight stiff alloy or composite, or fiber reinforced polymer. Thereference makes clear that relatively low weight is very important forthe proper functionality of the disclosed coordinate measurementmachine. A problem with such prior art coordinate measurement machineswas that their aluminum (or similarly lightweight material)construction, which has a significantly different thermal expansioncoefficient from that of the joint's bearings, causes variation in thejoint's rigidity over temperature. This reduces accuracy of measurementstaken over the operating temperature range.

The present invention takes an approach that may seem counterintuitive.In one embodiment, structural elements of the joints of the arm 2 may befabricated of steel matching the material from which the bearings 32, 34are fabricated. Structural elements in this context refer to housings28, 48, 49, and 78, shafts 30, 50, and 80, and shaft portions 50 a and50 c. These are the structural elements that are in contact with theinner or outer race of the ball bearings 32, 34. The housing 48 alsoattaches a swivel joint to the next hinge joint. Steel in this contextincludes stainless steel and has a thermal expansion coefficient in therange of between of 9.9 to 18 μm/m° C. at 25° C. The use of relativelyheavy steel for the structural elements of the joints of the arm 2 mayseem somewhat counterintuitive because, as discussed above, one of theimportant features of the CMM 1 is that it must be lightweight. Steel issignificantly heavier that the materials used by prior art coordinatemeasurement machines such as aluminum. Structural elements matching thematerial (i.e., steel) from which the bearings 32, 34 are fabricated,however, would have the same (or nearly the same) thermal expansioncoefficient (i.e., would expand or contract with temperature at the samerate) as the bearings 32, 34. This minimizes variation in the joint'srigidity over temperature and thus maintains accuracy of measurementstaken over the operating temperature range of the CMM 1.

In another embodiment, structural elements of the joints of the arm 2,other structural elements such as shaft portion 50 b, tubes 60, etc. andeven non-structural elements of the CMM 1 may be fabricated of acontrolled expansion alloy lighter in weight than steel but having athermal expansion coefficient matching that of chrome steel or 440 Cstainless steel (i.e., in the range of between of 9.9 to 18 μm/m° C. at25° C.). A commercially available example of such controlled expansionalloy is Osprey CE sold by Sandvik AB of Sandviken, Sweden. Structuralelements fabricated from materials matching the thermal expansioncoefficient (i.e., would expand or contract with temperature at the samerate) of the bearings 32, 34 minimize variation in the joint's rigidityover temperature and thus maintain accuracy of measurements taken overthe operating temperature range of the CMM 1. The significantly thinnerarm segments 8 and 9 fabricated from rigid yet relatively light materialsuch as, for example, carbon fiber or controlled expansion alloycombined with structural elements (and even non-structural elements)fabricated from controlled expansion alloy result in a CMM 1 that issignificantly lighter and significantly more accurate over the operatingtemperature range than prior art coordinate measuring machines.

FIG. 6A illustrates a cross-sectional view of exemplary hinge joint 14.Hinge joint 22 is very similar to hinge joint 18 described above. Hingejoint 14 is also similar to hinge joints 18 and 22, a significantdifference being that the hinge joint 14 includes a rotary damperassembly. In the illustrated embodiment of FIG. 6A, the rotary damperassembly is an instrumented assembly 90 a as described in detail below.To ease the use of the arm 2, a counter balance arrangement in the formof the rotary damper assembly 90 a may be provided to offset the torqueapplied by the weight of the articulated arm. The counter balanceprevents the articulated arm 2 from falling down rapidly due to its ownweight if the user releases it.

Conventionally, portable coordinate measuring machines used coil springsor torsion springs to counter balance the weight of the arm. See, forexample, U.S. Pat. Nos. 6,904,691 and 8,001,697 each of which is herebyincorporated by reference in their entirety. Another conventionalcounter balance systems included a piston or linear actuator assemblyforming a gas shock counterbalance. See, for example, U.S. Pat. No.8,402,669 which is hereby incorporated by reference in its entirety.Each of these conventional counter balance solutions had problems withadjustment and calibration of the counter balance. Also, theseconventional counter balance solutions were generally bulky and heavy,two undesirable characteristics for portable coordinate measuringmachines.

FIG. 6B illustrates an exploded view of the exemplary rotary damperassembly 90 a. The assembly 90 a includes the rotary damper 92 which maybe a commercially available rotary damper such as WRD dampersmanufactured by Weforma Dämpfungstechnik GmbH of Stolberg, Germany. Inone embodiment, the rotary damper 92 is a unidirectional rotary damperthat provides controlled damping of rotational movement of the shaftabout the axis of rotation in one direction of rotation. The assembly 90a may also include damper hub 94, damper sleeve 96, and torque sensorshaft hub 98, which together form an Oldham coupling. The assembly 90 amay also include torque sensor shaft 100. The assembly 90 a may alsoinclude spacer 102, mount 104, and hardware such as bolts 107 a-d and108 a-d. The mount 104 has four threaded apertures 110 a-d and fournon-threaded apertures 111 a-d.

As best seen in FIG. 6A, the damper assembly 90 a comes together byfirst coupling a portion of the torque sensor shaft 100 to the shaft 80of the hinge joint 14. A portion of the torque sensor shaft 100 may beinserted in and fixedly attached to (e.g., by using adhesive) the axialopening 80 a of the shaft 80. The mount 104 is coupled to the housing 78of the hinge joint 14 by inserting the bolts 108 a-d through theapertures 111 a-d and threading them into threaded openings in thehousing 78. The rest of the components of the rotary damper assembly 90a are then stacked in order: the shaft hub 98 on the shaft 100, thedamper sleeve 96 on the shaft hub 98, the damper hub 94 on the dampersleeve 96, and the damper hub 94 on the shaft 93 of the rotary damper92. The spacer 102 is sandwiched between the rotary damper 92 and themount 104 by threading the bolts 107 a-d to the threaded apertures 110a-d of the mount 104. Thus, the rotary damper 92 is operably coupled tothe shaft 80 and the housing 78.

The rotary damper 92 provides controlled damping of rotational movementof the shaft 80 about the axis of rotation b. The amount of torqueoutput to control damping provided by the rotary damper 92 may bepreadjusted and precalibrated to tight specifications. Thus, the rotarydamper assembly 90 a alleviates problems with adjustment and calibrationof counter balance that were typical to conventional counter balancesolutions for portable coordinate measuring machines such as coilsprings, torsion springs, and pistons. Also, the rotary damper assembly90 a provides a counter balance solution that is generally more compactand lighter in weight when compared to conventional counter balancesolutions such as coil springs, torsion springs, and pistons.

A potential issue that arises, particularly with use of a rotary damperto provide controlled damping of rotational movement, is that a user mayapply excessive torque to the arm 2 when moving it. The excessive forcemay effectively bend portions of the arm 2 affecting the ability of theCMM 1 to accurately detect the position of the measurement probe 6.Measurements taken under these conditions, in which the user essentiallymoves the arm too fast, may be inaccurate. The present disclosureprovides two potential solutions to this potential issue.

In the embodiment of FIGS. 6A and 6B, the rotary damper assembly 90 a isinstrumented to directly detect excessive torque at the joint 14. Themount 104 has webbing or spokes 104 a-d that connect the outer ring ofthe mount 104 which include the threaded apertures 110 a-d to the innerring of the mount 104 which include the non-threaded apertures 111 a-d.Installed on at least some of the spokes 104 a-d are strain gauges 106.Similarly, the torque sensor shaft 100 has webbing or spokes 100 a-dthat connect it to the torque sensor shaft hub 98. Installed on at leastsome of the spokes 100 a-d are strain gauges 106. The rotary damperassembly 90 a also includes a torque sensor PCB 112 which has installedthereon electronics that receive signals from the strain gauges 106.

Torque applied to the joint 14 is transmitted through the spokes 100 a-dand 104 a-d. Such torque manifests itself as rotational strain on thespokes 100 a-d and 104 a-d. Thus, by measuring strain at the spokes 100a-d and 104 a-d, the gauges 106 effectively sense strain at the shaft 80and the housing 78 of the joint 14 due to the rotational movement of theshaft 80 about the axis of rotation b. In that sense, the strain gauges106 are operably coupled to the shaft 80 and the housing 78. The straingauges output strain signals that circuitry in the PCB 112 or anothercircuit (e.g., the processor in the corresponding joint's PCB 36) in orexternal to the CMM 1 may use to detect and account for torque appliedto the joint 14.

Strain measured by the gauges 106 corresponds to an amount of torqueapplied to the joint 14. The measured strain, thus, also corresponds toan amount of bending or flexing of portions of the arm 2. The measuredstrain, therefore, may be correlated to an amount and nature of bendingor flexing of the arm 2 and that information, in turn, may be taken intoaccount when taking measurements with the CMM 1 to compensate forexcessive torque. Thus, in this instrumented embodiment of the rotarydamper assembly 90, an electrical circuit in the PCB 112 (or theprocessor in the corresponding joint's PCB 36 that receives the anglesignals from the read heads 68) may receive the strain signals (oramplified strain signals) from the strain gauges 106, convert thosesignals to corresponding bending or flexing of the arm 2 due to torqueapplied to the arm 2, and calculate the measurement at the measurementprobe 6 taking into account the corresponding bending or flexing of thearm 2. For example, the PCB 112 may include amplifiers to amplify theanalog signals from the strain gauges 106 and analog to digitalconverters to convert the amplified analog signals to digital signalsthat may be provided to a processor of the PCB 36 of the correspondingjoint. The processor may look up on a table or calculate an amount anddirection of bending or flexing of the arm 2 corresponding to thelocation and amplitude of the measured strain. Therefore, by measuringstrain at the spokes 100 a-d and 104 a-d, the CMM 1 can accuratelydetect the position of the measurement probe 6 regardless of a userapplying excessive torque to the arm 2.

In an alternative embodiment, when any of the strain signals or anagglomeration of the strain signals exceeds a certain strain threshold,a determination may be made that too much torque has been applied to thejoint 14. Based on that determination, the CMM 1 may disable the takingof measurements until after a certain amount of time (e.g., two to tenseconds) has passed. This is to allow for any portions of the arm 2 thatmay have bent due to the excessive applied torque to return to itsoriginal shape.

FIG. 6C illustrates an exemplary non-instrumented rotary damper assembly90 b. Unlike the rotary damper assembly 90 a of FIGS. 6A and 6B, therotary damper assembly 90 b is not instrumented to directly detectexcessive torque. In this embodiment, the angle signal output by theread heads 68 may be used to generate a speed signal that may be used asa proxy for applied torque. Torque applied to the arm 2 to move itgenerally corresponds to the speed at which the arm 2 moves. As statedabove, excessive torque applied to the arm 2 essentially corresponds tothe user moving the arm too fast, at too much speed. Therefore,excessive applied torque may be indirectly detected at the joints in theform of relatively high (i.e., too high) rotational speed. The readheads 68 output the angle signal that corresponds to the relative angleof rotation of the joint. The rate at which the measured angle ofrotation changes corresponds to the rotational speed of the joint.Detecting the rotational speed at the joint is a good proxy fordetecting applied torque. In this embodiment, the angle signal output bythe read heads 68 may be used to generate a speed signal by calculatingthe rate at which the measured angle of rotation changes, the speedsignal. A processor in the PCB 36 (or anywhere else) may measure thespeed signal (e.g., degrees per second) using a high resolution timer(e.g., 12.5 ns resolution) measuring the period of one of the encoder'squadrature signals. When the speed signal exceeds a certain rotationalspeed threshold, a determination is made that too much torque has beenapplied. Based on that determination, the CMM 1 may disable the takingof measurements until after a certain amount of time (e.g., two to tenseconds) has passed. This is to allow for any portions of the arm 2 thatmay have bent due to the excessive applied torque to return to itsoriginal shape.

The assembly 90 b is similar to assembly 90 a of FIGS. 6A and 6B. Theassembly 90 b may include the rotary damper 92. The assembly 90 b mayalso include the damper hub 94, damper sleeve 96, shaft hub 118(together forming an Oldham coupler), and shaft 120. The assembly 90 bmay also include spacer 122, mount 124, and hardware such as bolts 107a-d and 108 a-d. The spacer 122 is similar to the spacer 102 except thatit does not need to hold the PCB 112. The mount 124 has four threadedapertures 110 a-d and four non-threaded apertures 111 a-d. The mount 124is similar to the mount 104 except that it does not need the webbing orspokes 104 a-d.

The damper assembly 90 b comes together by first coupling a portion ofthe torque sensor shaft 120 to the shaft 80 of the hinge joint 14. Aportion of the torque sensor shaft 120 may be inserted in and fixedlyattached to (e.g., by using adhesive) the axial opening 80 a of theshaft 80. The mount 124 is coupled to the housing 78 of the hinge joint14 by inserting the bolts 108 a-d through the apertures 111 a-d andthreading them into threaded openings in the housing 78. The rest of thecomponents of the rotary damper assembly 90 b are then stacked in order:the shaft hub 118 on the shaft 120, the damper sleeve 96 on the shafthub 118, the damper hub 94 on the damper sleeve 96, and the damper hub94 on the shaft 93 of the rotary damper 92. The spacer 122 is sandwichedbetween the rotary damper 92 and the mount 124 by threading the bolts107 a-d to the threaded apertures 110 a-d of the mount 124. Thus, therotary damper 92 is operably coupled to the shaft 80 and the housing 78.

In one embodiment (not shown), instead of an add-on rotary damperassembly such as the assemblies 90 a and 90 b, rotary damping is builtinto the hinge joint 18. In this embodiment, a combination of a) thefirst bearing 32 or the second bearing 34 with b) the shaft 80 or thehousing 78 provides controlled damping of rotational movement of theshaft 80 about the axis of rotation b.

FIG. 7A illustrates a perspective view of an exemplary measurement probe6 a. Probe 6 a includes a housing 126 that has an interior space forhousing PCB 130 and a handle 128 that has an interior space for housingPCB 125. The housing 126 and the handle 128 are shown in FIG. 7Atransparent for illustration purposes. Housing 126 operably couples tothe swivel joint 24 (see FIGS. 1A-1D). Thus, the probe 6 a rotates aboutthe axis a of the swivel joint 24 and the swivel joint 24 detects theangle of rotation of the probe 6 a about the axis a.

The measurement probe 6 a may also include a probe stem assembly 136having a probe connector 138 at one end and a probe 140 at the otherend. The probe connector 138 connects to the housing 126 and the PCB130. The probe stem assembly 136 may be a touch trigger assembly whichtriggers the capture of the position of the probe 140 when the probe 140touches an object. The PCB 130 receives such a trigger signal andtransmits it as described below. The probe stem assembly 136 may alsohouse electronics such as, for example, an integrated circuit (e.g.,EEPROM) having stored therein a serial number to uniquely identify aprobe stem assembly 136 upon installation to the CMM 1.

Handle 128 may include two switches, namely a take switch 131 and aconfirm switch 132. These switches may be used by the operator to take ameasurement (take switch 131) and to confirm the measurement (confirmswitch 132) during operation. The handle 128 is generally shaped toresemble a person's grip, which is more ergonomic than at least someprior art probes. The handle 128 may also house a switch PCB 134 towhich the switches 131 and 132 may mount. Switch PCB 134 is electricallycoupled to PCB 125 hosting components for processing signals from theswitches 131 and 132. In one embodiment, the PCB 125 includes a wireless(e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of an electricalconnection to the communication bus of the CMM 1) that wirelesslytransmits take and confirm signals associated with the switches 131 and132 to, for example, a host PC that generally controls the CMM 1.Wireless transmission of the take and confirm signals associated withthe switches 131 and 132 significantly simplifies construction andwiring of the probe 6 a.

The measurement probe 6 a may also include an option port 142 to whichoptional devices such as, for example, a laser scanner (not shown) maybe connected. The option port 142 provides mechanical connections forthe optional devices to be supported by the measurement probe 6 a. Theoption port 142 may also provide electrical connections for the optionaldevices to interface with the communication bus of the CMM 1.

FIG. 7B illustrates a perspective view of an exemplary alternativemeasurement probe 6 b. The probe 6 b is similar to the probe 6. Theprobe 6 b, however, includes a different housing 127 and handle 129.Unlike the probe 6, the housing 127 of the probe 6 b includes aconnecting portion 143 that may connect directly to the hinge joint 22.Thus, when the probe 6 b is used, the swivel joint 24 is not used. Thehousing 127 and the probe stem assembly 136 do not rotate about the axisa. The housing 127 and the probe stem assembly 136 are fixed about theaxis a. The handle 129, on the other hand, includes a connecting portion144 that rotatably couples the handle 129 to the housing 127. Thus, thehandle 129 rotates about the axis a. Like the handle 128 of probe 6, thehandle 129 has an interior space for housing PCB 125. The PCB 125 mayinclude a wireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (insteadof an electrical connection to the communication bus of the CMM 1) thatwirelessly transmits signals such as, for example, take and confirmsignals associated with the switches 131 and 132. Thus, the handle 129is rotatably coupled to the arm 2 to rotate about the axis a but,importantly, the handle 129 is not electrically coupled to the arm 2because signal transmission is accomplished wirelessly.

The probe 6 b is a significant advance in the coordinate measuringmachine field because it alleviates the need for seven true axes ofrotation. The CMM 1 as illustrated in FIGS. 1A-1 D include seven trueaxes of rotation (i.e., axes associated with joints 12, 14, 16, 18, 20,22, and 24). Including seven true axes of rotation results in arelatively more complex and expensive CMM 1. The rotatable handle 129,mechanically and wirelessly (but not electrically) connected to the arm2 and thus not requiring the seventh joint 24, alleviates the need for a“true” seventh axis because it permits the handle 129 to rotate asneeded for hand position without the complexity of a seventh set ofbearings, transducers, electronics, etc.

FIG. 8 illustrates a perspective view of an exemplary on-arm switchassembly 10. Switch assembly 10 includes a housing 146 that has opening148 to mount (e.g., clamp) the switch assembly 10 to the arm segment 8or, alternatively to the arm segment 9. The housing 146 has an interiorspace for housing a PCB. Similar to the probes 6 and 6 b, the switchassembly 10 may include two switches, namely a take switch 131 and aconfirm switch 132 that may be used by the operator to take ameasurement (take switch 131) and to confirm the measurement (confirmswitch 132) during operation. The position of the on-arm switch assembly10, and more importantly of the switches 131 and 132, on the arm 2instead of in the handles of the probe 6 allow for the operator to moveand position the measurement probe 6 with one hand and to actuate theswitches 131 and 132 with the other hand while supporting the arm. Priorart coordinate measurement machines required operators to position themeasurement probe and actuate measurement switches in the probe with thesame hand. This is not ergonomic. The on-arm switch assembly 10 is asignificant advance in the coordinate measuring machine field because itprovides a significantly more ergonomic solution as compared to priorart coordinate measurement machines.

The on-arm switch assembly 10 may also house a switch PCB 134 to whichthe switches 131 and 132 may mount or the on-arm switch assembly 10 mayinclude a PCB that incorporates the functionality of both PCB 130 andswitch PCB 134. In one embodiment, the PCB in the on-arm switch assembly10 electrically connects to the communication bus of the CMM 1. Inanother embodiment, the PCB in the on-arm switch assembly 10 includes awireless (e.g., Wi-Fi, Bluetooth, etc.) transmitter (instead of anelectrical connection to the communication bus of the CMM 1) thatwirelessly transmits take and confirm signals associated with theswitches 131 and 132.

FIG. 9 illustrates a block diagram of exemplary electronics for the CMM1. The CMM 1 may include external communication interfaces such as aUniversal Serial Bus (USB) 150 and wireless (Wi-Fi) 152. The CMM 1 mayalso include an internal communication bus (e.g., RS-485) 154. Asdiscussed above, the various joints or axis of the CMM 1 each includes aPCB 36 which has installed thereon at least one transducer configured tooutput an angle signal corresponding to an angle of rotation of thejoint. The PCB 36 may each include a processor 70 for receiving andprocessing angle signals from the transducers and/or strain signals fromthe PCB 112 of the rotary damper assemblies 90. The PCB 36 may alsoinclude a transceiver 156 to interface with the bus 154. The PCB 130 ofthe measurement probe 6, which may carry signals from the touch triggerprobe 140, may also connect to the communication bus 154. The bus 154may also connect to the option port 142 of the measurement probe 6 tocommunicate/control optional devices such as, for example, a laserscanner installed to the option port 142. The PCB 125 of the handle 128may wirelessly transmit take and confirm signals associated with theswitches 131 and 132.

The bus 154 terminates at a main PCB 158 preferably located at the base4 of the CMM 1. The main PCB 158 includes its own main processor 160 andtransceiver 162 for connecting to the bus 154. The main PCB 158 receivesthe angle signals from the transducers in the CMM 1 and output anagglomeration of the received angle signals via the USB 150 or the Wi-Fi152 to a host PC such that the host PC may calculate the position of themeasurement probe 6 based on this information and other informationrelating to the CMM 1 (e.g., location, length of arm segments, etc.) Theinternal bus 154 may be consistent with RS485.

Prior art coordinate measuring machines configured to use an RS485internal bus incorporated dedicated capture and trigger wires totransport capture and trigger signals, respectively. See, for example,U.S. Pat. No. 6,219,928, which is hereby incorporated by reference inits entirety. A capture signal is a synchronous signal generated by amaster controller in the RS485 arrangement. A trigger signal is anasynchronous signal that is generated by devices attached to thearticulated arm such as a touch trigger probe accessory (e.g., RenishawTP20). The dedicated trigger wire travels from the probe to the mastercontroller in the base of the articulated arm. The trigger signal thattravels through the dedicated trigger wire interrupts the mastercontroller. An interrupt service routine in the master controllergenerates a synchronous capture signal to capture angle signals from theencoders

Note that in FIG. 9 there are no dedicated capture or trigger wires.Instead the bus 154 includes, from the main PCB 158's point of view, apair of bidirectional wires 164 and 166 (A-B Pair, half duplex) or twopairs of unidirectional wires (A-B Pair and Y-Z pair, full duplex).

Even with the use of steel for the structural elements of the joints asdescribed above, the arm 2 remains relatively lightweight partly becausemany of its components (e.g., shafts, bearings, housings, arm segments,etc.) are smaller than those of prior art coordinate measuring machines.Compare, for example, the shafts, housings, and arm segments of the CMM1 disclosed herein to corresponding elements of the coordinate measuringmachines disclosed in U.S. Pat. No. 8,607,467. The smaller components ofthe CMM 1 have significantly less mass and are, thus, significantlylighter than their prior art counterparts. Smaller components may beused in the CMM1 in part because the amount of wires to carry signalswithin the CMM 1 has been significantly reduced when compared to priorart coordinate measuring machines. Prior art coordinate measuringmachines needed significant space within shafts, housings, arm segments,etc. to route wires. Because of the arrangement of the electronics asdescribed in FIG. 9 and the timing signals as described below, wiringmay be significantly reduced in the CMM 1, which contributes to itslight weight.

FIG. 10A illustrates an exemplary timing chart of the exemplaryelectronics of FIG. 9 in operation. In operation, the main processor 160may send (via wires 164 and 166) a capture command at predeterminedintervals (e.g., 960 microseconds) to the processors 70 of the encoderPCB 36. As seen in FIG. 10A, each processor 70 receives the capturecommand. In response, an interrupt service routine in the processor 70generates an internal capture with a fixed calibrated latency amongencoder PCB 36 of, for example, 1.2 microseconds. As shown in FIG. 10A,the internal capture pulse may be active low (or activate high as shownin some of the other exemplary timing diagrams) and have a typicallength of, for example, 5 microseconds

FIG. 10B illustrates another exemplary timing chart of the exemplaryelectronics of FIG. 9 in operation. In operation, the main processor 160may send (via wires 164 and 166) capture commands at predeterminedintervals (e.g., 960 microseconds) to each of the processors 70 of theencoder PCB 36. As seen in FIG. 10B, each processor 70 receives theircapture command. At (1) the first encoder processor 70 enables theserial line interrupt 8 data bytes or 11 μs (8*11 bits/data byte*125ns/bit) after receiving its capture command. At (2) the second encoderprocessor 70 enables the serial line interrupt 7 data bytes or 9.625(˜9.63) μs after receiving its capture command and so on for the thirdto sixth encoder processors 70. At (7) the 7^(th) encoder processor 70enables the serial line interrupt 2 data bytes or 2.75 μs afterreceiving its capture command. At (8) option port processor 70 enablesthe serial line interrupt 1 data byte or 1.375 (˜1.38) μs afterreceiving its capture command. Next, at (9), the main processor 160sends a read data command to the first encoder processor 70, a hardwareinterrupt is generated on the falling edge of the start bit, and aninterrupt service routine in the processor 70 generates an internalcapture in about 0.19 μs. As shown in FIG. 10B, the internal capturepulse may be active high (or active low as shown in some of the otherexemplary timing diagrams) and have a typical length of, for example, 4microseconds.

FIG. 10C illustrates another exemplary timing chart of the exemplaryelectronics of FIG. 9 in operation. As shown in FIG. 10C, the processor70 could initiate an internal capture 1.38 microseconds after receivingthe last capture command. This method may have a larger error than someof the methods described above mostly due to clock errors introduced bythe use of different processors 70.

FIG. 10D illustrates another exemplary timing chart of the exemplaryelectronics of FIG. 9 in operation. As shown in FIG. 10D, in dual pair(A-B pair and Y-Z pair, full duplex) serial configuration, once thecapture command is received by the encoder processors 70, each processor70 enables the serial line interrupt. Next, the main processor 160 sendsa read data command to the first encoder processor 70, a hardwareinterrupt is generated on the falling edge of the start bit, and aninterrupt service routine in the processor 70 generates an internalcapture in about 0.19 μs.

FIG. 10E illustrates another exemplary timing chart of the exemplaryelectronics of FIG. 9 in operation. As shown in FIG. 10E, in dual pair(A-B pair and Y-Z pair, full duplex) serial configuration, once acapture command is received by an the encoder processors 70, eachprocessor 70 can immediately initiate an Internal Capture with a typicallatency of 1.63 microseconds. This method is less precise than some ofthe methods described above due to the variation in clock frequency ofprocessors 70.

As shown in FIG. 10F, on PCB 130 the interrupt service routine forcapture command (n), stores and resets an interval timer/counter. Theasynchronous trigger from, for example, the touch trigger probeaccessory captures and stores the value of the interval timer/counter.On the subsequent capture command (n+1), the interval timer/counter isstored and reset.

To find the position of the probe 6 at the time the asynchronoustrigger, the vector difference between positions (n) and (n+1) may bemultiplied by the ratio of the asynchronous trigger captured valuedivided by the (n+1) position captured value and added to the position(n) vector. In an alternative embodiment, the asynchronous trigger mayalso have a fixed calibrated latency, which may be subtracted from theasynchronous trigger captured value to arrive at the true position. Inanother embodiment, an asynchronous trigger port (not shown) at the baseof the arm may be use to trigger an internal timer/counter in the mainprocessor 160.

Thus, by accounting and correcting for latency at each PCB 36, theelectronics of the CMM 1 may take accurate measurements withoutrequiring dedicated capture and trigger wires.

Definitions

The following includes definitions of selected terms employed herein.The definitions include various examples or forms of components thatfall within the scope of a term and that may be used for implementation.The examples are not intended to be limiting. Both singular and pluralforms of terms may be within the definitions.

As used herein, an “operable connection” or “operable coupling,” or aconnection by which entities are “operably connected” or “operablycoupled” is one in which the entities are connected in such a way thatthe entities may perform as intended. An operable connection may be adirect connection or an indirect connection in which an intermediateentity or entities cooperate or otherwise are part of the connection orare in between the operably connected entities. In the context ofsignals, an “operable connection,” or a connection by which entities are“operably connected,” is one in which signals, physical communications,or logical communications may be sent or received. Typically, anoperable connection includes a physical interface, an electricalinterface, or a data interface, but it is to be noted that an operableconnection may include differing combinations of these or other types ofconnections sufficient to allow operable control. For example, twoentities can be operably connected by being able to communicate signalsto each other directly or through one or more intermediate entities likea processor, operating system, a logic, software, or other entity.Logical or physical communication channels can be used to create anoperable connection.

“Signal,” as used herein, includes but is not limited to one or moreelectrical or optical signals, analog or digital signals, data, one ormore computer or processor instructions, messages, a bit or bit stream,or other means that can be received, transmitted, or detected.

To the extent that the term “includes” or “including” is employed in thedetailed description or the claims, it is intended to be inclusive in amanner similar to the term “comprising” as that term is interpreted whenemployed as a transitional word in a claim. Furthermore, to the extentthat the term “or” is employed in the detailed description or claims(e.g., A or B) it is intended to mean “A or B or both”. When theapplicants intend to indicate “only A or B but not both” then the term“only A or B but not both” will be employed. Thus, use of the term “or”herein is the inclusive, and not the exclusive use. See, Bryan A.Garner, A Dictionary of Modern Legal Usage 624 (2d. Ed. 1995).

While example systems, methods, and so on, have been illustrated bydescribing examples, and while the examples have been described inconsiderable detail, it is not the intention of the applicants torestrict or in any way limit scope to such detail. It is, of course, notpossible to describe every conceivable combination of components ormethodologies for purposes of describing the systems, methods, and soon, described herein. Additional advantages and modifications willreadily appear to those skilled in the art. Therefore, the invention isnot limited to the specific details, the representative apparatus, andillustrative examples shown and described. Thus, this application isintended to embrace alterations, modifications, and variations that fallwithin the scope of the appended claims. Furthermore, the precedingdescription is not meant to limit the scope of the invention. Rather,the scope of the invention is to be determined by the appended claimsand their equivalents.

What is claimed is:
 1. A portable coordinate measurement machine (CMM)comprising: a manually-positionable articulated arm having first andsecond ends, the articulated arm including a plurality of arm segmentsand a plurality of rotary joints, the first end including a connectorconfigured to connect to a measurement probe and the second endincluding a base; wherein at least one of the rotary joints includes:first and second bearings; a shaft that engages an inner diameter of thefirst bearing and an inner diameter of the second bearing, the shaftconfigured to rotate about an axis of rotation of the first bearing andthe second bearing; a housing having at least one port that engages atleast one of an outer diameter of the first bearing and an outerdiameter of the second bearing; at least one transducer configured tooutput an angle signal corresponding to an angle of rotation of theshaft relative to the housing about the axis of rotation; and a rotarydamping mechanism configured to provide controlled damping of rotationalmovement of the shaft about the axis of rotation.
 2. The CMM of claim 1,wherein the rotary damping mechanism includes: a rotary damper operablycoupled to the shaft and the housing.
 3. The CMM of claim 1, wherein therotary damping mechanism includes: rotary damping built into the atleast one of the rotary joints.
 4. The CMM of claim 1, wherein the atleast one of the rotary joints includes: a circuit operably connected tothe at least one transducer and configured to output a speed anddirection signal corresponding to the speed of the rotational movementof the shaft about the axis of rotation.
 5. The CMM of claim 1, whereinthe at least one of the rotary joints includes: at least one straingauge operably coupled to at least one of the shaft and the housing andconfigured to sense strain on the at least one of the shaft or thehousing due to the rotational movement of the shaft about the axis ofrotation and to output a strain signal.
 6. The CMM of claim 1, whereinin at least one joint of the plurality of joints a) the shaft thatengages the inner diameter of at least one of the first bearing and thesecond bearing and b) the port of the housing that engages the outerdiameter of at least one of the first bearing and the second bearing arefabricated of steel, or a first joint, from the plurality of joints, isattached to a second joint, from the plurality of joints, by a steelstructure that is in contact with the inner or outer race of a bearingof the first joint or the inner or outer race of a bearing of the secondjoint, or all structural portions of at least one of the plurality ofrotary joints are fabricated of steel.
 7. The CMM of claim 1, whereinany structural portions of the CMM including the plurality of armsegments and the plurality of rotary joints are fabricated of acontrolled expansion alloy lighter in weight than steel and having athermal expansion coefficient matching that of steel or stainless steelin the range of between of 9.9 to 18 μm/m° C. at 25° C.
 8. The CMM ofclaim 1, the measurement probe including a handle mechanically but notelectrically operably coupled to the first end, the handle rotatablycoupled to the first end to rotate about a central axis of themeasurement probe, the handle including: a wireless transmitter; and atleast one switch button operably connected to the wireless transmitterand configured to, when pressed, cause the wireless transmitter totransmit a wireless signal that corresponds to the CMM taking ameasurement.
 9. The CMM of claim 1, comprising: an electrical circuitincluding a serial communication circuit configured without a dedicatedcapture wire to receive the angle signal and other signals from othertransducers in the CMM, the electrical circuit configured to output anagglomeration of the angle signal and the other signals to provideinformation corresponding to a position of the measurement proberelative to the base.
 10. A portable coordinate measurement machine(CMM) comprising: an articulated arm having first and second ends, thearticulated arm including a plurality of arm segments and a plurality ofrotary joints, the first end configured to connect to a measurementprobe and the second end configured to connect to a base; wherein atleast one of the rotary joints includes: first and second bearings; ashaft configured to rotate about an axis of rotation of the firstbearing and the second bearing; a housing having at least one port thatengages at least one of an outer diameter of the first bearing and anouter diameter of the second bearing; and a rotary damper operablycoupled to the shaft and the housing and configured to providecontrolled damping of rotational movement of the shaft about the axis ofrotation.
 11. The CMM of claim 10, wherein the at least one of therotary joints includes: at least one transducer configured to output anangle signal corresponding to an angle of rotation of the shaft relativeto the housing about the axis of rotation; and a circuit operablyconnected to at least one transducer and configured to output a speedsignal corresponding to the speed of the rotational movement of theshaft about the axis of rotation based on the angle signal and time, thecircuit further configured to compare the speed signal to apredetermined speed threshold to determine whether the rotationalmovement occurred at excessive speed or as a result of excessive torque.12. The CMM of claim 10, wherein the at least one of the rotary jointsincludes at least one strain gauge operably coupled to at least one ofthe shaft and the housing and configured to sense strain on the at leastone of the shaft and the housing due to the rotational movement of theshaft about the axis of rotation and to output a strain signal based onwhich location of the measurement probe is at least in part calculated.13. The CMM of claim 10, comprising: at least one transducer configuredto output an angle signal corresponding to an angle of rotation of theshaft relative to the housing about the axis of rotation; and anelectrical circuit including a serial communication circuit configuredwithout a dedicated capture wire to receive the angle signal and otherangle signals from other transducers in the CMM, the electrical circuitconfigured to output an agglomeration of the angle signal and the otherangle signals to provide information corresponding to a position of themeasurement probe relative to the base.
 14. The CMM of claim 10, whereinthe shaft has no portion whose diameter is larger than the innerdiameter of the first bearing or the inner diameter of the secondbearing, or the at least one port of the housing has no portion whosediameter is narrower than the outer diameter of the first bearing or theouter diameter of the second bearing.
 15. A portable coordinatemeasurement machine (CMM) comprising: an articulated arm having firstand second ends, the articulated arm including a plurality of armsegments and a plurality of rotary joints, the first end configured toconnect to a measurement probe and the second end configured to connectto a base; wherein at least one of the rotary joints includes: at leastone bearing; a shaft configured to rotate about an axis of rotation ofthe at least one bearing; a housing having at least one port thatengages an outer diameter of the at least one bearing; and rotarydamping built into the at least one of the rotary joints.
 16. The CMM ofclaim 15, wherein the at least one of the rotary joints includes: atleast one transducer configured to output an angle signal correspondingto an angle of rotation of the shaft relative to the housing about theaxis of rotation; and a circuit operably connected to at least onetransducer and configured to output a speed signal corresponding to thespeed of the rotational movement of the shaft about the axis of rotationbased on the angle signal and time, the circuit further configured tocompare the speed signal to a predetermined speed threshold to determinewhether the rotational movement occurred at excessive speed or as aresult of excessive torque.
 17. The CMM of claim 15, wherein the atleast one of the rotary joints includes at least one strain gaugeoperably coupled to at least one of the shaft and the housing andconfigured to sense strain on the at least one of the shaft and thehousing due to the rotational movement of the shaft about the axis ofrotation and to output a strain signal based on which location of themeasurement probe may be at least in part calculated.
 18. The CMM ofclaim 15, wherein in at least one joint of the plurality of joints a)the shaft and b) the port of the housing are fabricated of steel. 19.The CMM of claim 15, wherein a first joint, from the plurality ofjoints, is attached to a second joint, from the plurality of joints, bya steel structure that is in contact with the inner or outer race of abearing of the first joint or the inner or outer race of a bearing ofthe second joint.
 20. A portable coordinate measurement machine (CMM)comprising: an articulated arm having first and second ends, thearticulated arm including a plurality of arm segments and a plurality ofrotary joints, the first end configured to connect to a measurementprobe and the second end configured to connect to a base; wherein atleast one of the rotary joints includes: a shaft configured to rotateabout an axis of rotation of the at least one of the rotary joints; anda rotary damping mechanism configured to provide controlled damping ofrotational movement of the shaft about the axis of rotation.